Effect of forewing sweeping on aerodynamic performance of butterfly like model

The wing of a butterfly consists of partially overlapping forewing and hindwing, and forewing sweeping can dynamically change the shape of the whole wing. In this work, the effect of forewing sweeping on aerodynamic performance of a butterfly like model is studied using a solver based on immersed boundary method and adaptive mesh. For aerodynamic performance, adding a “forward-backward-forward” sweeping motion to the forewing makes it more suitable for fast cruising flight, and compared to the situation without forewing sweeping, the drag is reduced by 46% and the lift to drag ratio is increased by 45%. On the contrary, adding a “backward-forward-backward” sweeping motion to the forewing increases lift and makes it more suitable for climb flight. For downstroke and middle to late upstroke, the forewing sweeping affects the Leading-Edge Vortex (LEV) through two factors: sweeping velocity and forward sweeping angle, and their effects are coupled. A large forward sweeping velocity can enhance the strength of LEV, while a large forward sweeping angle can weaken it. For early upstroke, the forewing sweeping can affect the wake capture mechanism, sweeping backward can enhance it while sweeping forward can weaken it. The findings in this work provide insight into the design of butterfly like Micro Air Vehicles (MAVs).